As long as the customers were nice and respectful then there can never be too big of a tip! Honestly the reason she tipped you so much is because not only does it make you happy it made her happy. Sometimes people like to leave large tips because maybe they worked a restraunt through college and know it's tough, or sometimes it's even something as simple as your reminded them of their daughter and it made them happy. But when people leave big tips they are happy to do so. If she gave you a hug then it just means you gave her great service and it made her enjoy her evening out. So I say don't feel guitly and enjoy the extra cash!